This invention relates to fluid operated clutches wherein clutch capacity is proportional to input speed.
Prior art of possible relevance includes U.S. Letters Pat. Nos. 3,831,726 to Woody et al, issued Aug. 27, 1974; 3,863,746 to Schulz, issued Feb. 4, 1975; and 3,872,956 to Herr et al, issued Mar. 25, 1975.
Fluid operated clutches of the type wherein a centrifugal head on a rotating column of hydraulic fluid is utilized to force a piston against a clutch pack and engage the clutch have been of significant value in marine propulsion systems. One of the main advantages of such clutches is the fact that clutch capacity is related to input or engine speed. This feature ensures against propulsion engine reversal caused by propeller inertia feedback through a fully engaged reverse clutch.
With conventional clutches, the capacity at a set control pressure is constant and totally independent off engine speed. If the engine for the load is throttled back and the selector valve reversed, engine reversal will occur. Propeller inertia feeds torque back through the clutch at some value and due to its set capacity, the clutch will carry the torque back to the engine which, at a low speed, will have a low torque output. As a consequence, the engine cannot carry the feed back torque and is forced into reverse rotation.
In the case of fluid operated clutches of the type mentioned above, the clutch capacity is related to input or engine speed and can be set so that the capacity is always less than available engine torque at any given engine speed. As a consequence, propeller inertia feedback cannot occur, thereby allowing the elimination of the usual propeller shaft brake.
Heretofore, however, such clutches have not been susceptible to universal use in that the capacity is limited by available rotational speed and clutch diameter. Therefore, they cannot be utilized with transmissions of various sizes or having various output speeds.